Method of preparing polyacrylonitrile fibers



Aug, 23, 1966 o. SUNDEN ETAL METHOD OF PREPARING POLYACRYLONITRILEFIBERS Filed March 7, 1962 United States Patent 3,268,490 METHOD OFPREPARING POLYACRYLO- NlTRllLE FIBERS Olof Sunden, Kyrkvagen 26A,Lidingo 1, Sweden; Sten Erik Arne Lennart Tunefors, Ljungaverk, Sweden;and gvenl Hugo Siinnerskog, Parkgatan 40, Bramhult,

we en Filed Mar. 7, 1962, Ser. No. 177,957 6 Claims. c1. 26tl78.5)

INTRODUCTION This invention generally relates to new compositions whichare particularly useful for forming filaments, yarns, fibers and films.More specifically this invention pertains to new polymer compositionswhich contain predominant amounts of acrylonitrile and which arecross-linked to a critically small extent so that such compositions canbe wet-spun at a higher spinning rate while permitting stretching of thefiber during the coagulation step and ensuring improved properties ofthe product. This invention also relates to methods for preparing andusing the aforesaid compositions. (The term polymer when used herein isintended to encompass both homopolymers and copolymers in accordancewith prevailing plastic nomenclature.)

BACKGROUND Whereas fibers containing acrylonitrile have been prepared bydry-spinning polymer solutions in heated air, in recent years thewet-spinning of such fibers has been practiced because of the moredesirable properties of the products which can be obtained bywet-spinning. In Wetspinning, a viscous solution of a polymer in apolymer solvent is extruded through a spinneret into a coagulating bathwherein the polymer solvent is simultaneously released to (or extractedinto) the coagulating bath as the fiber is formed. The fiber isthereafter usually stretched while still in the coagulating bath inorder to orient the molecules of the fiber and to improve the extractionof the solvent.

Polymers containing 100 percent of acrylonitrile in the molecule aregenerally not used, since such polymers are ditficult to dye by commonmethods. Accordingly, copolymers containing up to 30 percent of anothercopolymerizing unsaturated compound, such as, for example vinylacetate,methacrylonitrile, acrylates and methacrylates, unsaturated tertiaryamines or unsaturated sulphonic acids and sulphones are usuallyemployed.

The most common polymer solvents are N,N-dimethylformamide,N,N-dimethylacetamide, dimethylsulfoxide, butyrolactone, ethylenecarbonate and N,N-dimethylmethoxyacetamide.

A number of different coagulating liquids are known in the art. The arthas also recognized that the various coagulation liquids have differingpowers to coagulate insofar as acrylonitrile polymer solutions areconcerned.

Among the most common coagulating liquids may be mentioned water,concentrated aqueous solutions of electrolytes, isopropanol, glycerineand aqueous solutions of the polymer solvent used. Pure water andglycerine are known to have high coagulation (i.e. solvent extracting)power, but rapid coagulation makes the formed fiber so brittle andspongy and of such low tensile strength that it cannot be appreciablystretched during coagulation without the risk of fiber rupture andimpairment of the me chanical properties of the fiber.

It is also known that aromatic hydrocarbons such as benzene, toluene andcymene or hydrocarbon mixtures containing more than 50 percent aromatichydrocarbons can be used as coagultants. Such coagulants have a somewhatlower coagulation power than pure water and glycerine and this lowercoagulation power is beneficial in that it insures a gradual coagulationand makes it possible to stretch the formed fiber in the coagulationbath in order to orient the molecules and impart tensile strength.However, aromatic hydrocarbons are disadvantageous as coagulants sincethey are partially soluble in the polymer and cause both a certainporosity in the fiber and a loss of its abrasion resistance.

Hydrocarbon coagulants containing less than 50 percent by weight ofaromatic hydrocarbons (for example hydrocarbon containing more than 50percent by weight of aliphatic hydrocarbonssuch as kerosene hydrocarbonswith a boiling point of to 300 C.) avoid some of the disadvantages ofhydrocarbons having more than 50 percent aromatics, but they suffer fromthe disadvantage that they have a very slow coagulation rate andspinning rate owing to the very slow development of fiber strength. Thisslow spinning rate in eifect limits the production output for any plant.

Acrylic fibers have many favorable properties in comparison with othersynthetic fibers. For example acrylic fibers have a wool-like hand,warmth and comfortness. However, the acrylic fibers are less thanperfect in the following four aspects:

(1) They show fibrillation (i.e. splitting of fibers into thinnerfibrils during wearing); (2) Their wrinkle recovery properties are notas good as natural wool; (3) Their dimensional stability and pleatretention are not as good as polyester fibers; (4) They are sensitive tosoiling.

Many attempts have been made to improve the above mentioned properties.The only known way of diminishing the tendency toward fibrillation is todecrease the orientation of the fiberbut this results in lower fiberstrength. In order to improve the wrinkle recovery, the dimensionalstability and the pleat retention properties it has been found necessaryto use a polymer composition which has a low degree of plasticity underweaning and washing conditions-but the ditficulty with this is that afiber made from such a polymer is inferior with respect to its dyeingproperties. Thus, while it has been possible to improve one or two ofthe above-mentioned properties, such improvement has only been possiblebecause other valuable properties of the fiber have been sacrificed.

OBJECTS It is therefore a primary object of this invention to provide anacrylonitrile polymer composition which can be readily spun in what havetheretofore been considered as slow-acting coagulants while at the sametime permitting stretching to develop better extraction of the solventand better fiber properties. i

Another object of the present invention is to improve the spinnabilityof the spinning dope in slow-acting coagulating baths and to improve themechanical and physical propertiesparticularly at elevatedtemperaturesof fibers and filaments prepared from polyacrylonitrile, byusing a fiber-forming completely soluble, acrylonitrile polymer which iscross-linked to a certain low degree.

Another object is to diminish the fibrillation tendency of the fiber.Fibers made of the polymer composition of the present invention haveless tendency to fibrillate during wearing even when the fiber has ahigh strength. A high degree of stretching in the production of thefiber will give the higher strength of the fiber even when said polymercomposition is used. The molecular orientation measu-red with X-raymethods, however, does not increase with the stretching at the same rateas for linear polymers and the resulting fiber will not fibrillate asmuch as a fiber made of a linear polymer.

Still another object of the present invention is to improve the wrinklerecovery, dimensional stability and pleat retention properties of thefiber. These properties mainly depend on the high degree of plasticityof acrylic fibers at a temperature of 3540 C. and the humidity conditionclose to the skin of the human body. The composition of the polymer ofthe present invention contributes to improved elastic properties of thefiber and to decreased plastic properties, which result in theimprovements mentioned.

Finally, an object of the invention is to produce fibers with excellentsoil and stain resistance. Dry soiling is said to depend on staticelectricity, but in fact the surface of the fiber is more responsiblefor the soiling properties than the static properties. By using aslow-acting coagulant, such as one containing more than 50 percentaliphatic hydrocarbons, a very smooth and tight fiber surface isachieved without longitudinal cracks or surface porosity. Cracks andporosity are unavoidable with other synthetic fibers and they areresponsible for the severe soil retention of the fibers as well as fatand wet staining. By the combination of coagulation in hydrocarbons andthe polymer structure composition of the present invention it has beenpossible to improve the soil resistance and also the stain resistance ofthe fiber to a degree not previously achieved.

These and other objects and advantages will become more apparent afterreading the following description and claims taken in conjunction withthe drawing.

THE PRESENT INVENTION We have found according to this invention that itis possible to produce acrylonitrile polymers of unexpected utility andnovel properties composed of at least 85 molar percent of acrylonitrileunits and a total of from to about molar percent of one or severalmonoethyleni" cally unsaturated monomer units copolymerizable withacrylonitrile and cross-linked to a certain very limited degree with across-linking polyethylenically unsaturated monomer.

Examples of satisfactory monoet-hylenically unsaturated monomers wouldinclude vinyl acetate, vinyl chloride, vinylidene chloride, acrylicacid, acrylamide, methacrylonitrile, methacrylamide or an ester ofacrylic acid and methacrylic acid such as methylacrylate or anunsaturated sulphonic acid. While the broad range of this monomer is0-15 percent, a more preferred range is 2-8 or 2-10 molar percent. Ofthe above-mentioned monomers, we have found acrylic acid, acrylic estersand acrylic amide as well as methacrylic acid, their esters andmethacrylic amide, to be the most suitable. The advantage of theselatter compounds compared with the others lies in the fact that theygive the fiber good dyeability, primarily with basic dyes, atconcentrations as low as 2-8 molar percent in the copolymer.Furthermore, their copolymerization rates with acrylonitrile make iteasy to prepare copolymers with a relatively homogeneous composition.The comonomer can be randomly distributed in the polymer, but graft andblock polymers also seem to be suitable.

For improving the dyeabiilty more than one comonomer should be used, forexample methylacrylate and an unsaturated sulphonic acid.

The cross-linking polyethylenically unsaturated monomer is preferablyeither divinyl benzene, methylenbisacrylamide, diallyl phthalate,diallylmaleate, ethylene acrylate, ethylene diacrylate ortriacrylylperhydrotriazine. Methylenebisacrylamide andtriacrylylperhydrotriazine may be prepared by reacting acrylonitrile andformaldehyde in the presence of sulphuric acid.

The cross-linking of the polymer may be accomplished in a number ofways. The simplest procedure is to polymerize acrylonitrile in thepresence of small amounts of the polyfunctional unsaturatedcross-linking compounds. It is important that the cross-linking agent isevenly distributed in the polymer. When the cross-linking is nothomogeneously distributed, highly cross-linked polymer particles areobtained which do not dissolve in dimethylformamide or other commonsolvents for acrylonitrile polymers and which form gel-lumps or stronglyswellable microgel particles, causing troublesome clogging of filtersand spinnerets. The cross-linking agents named above have the advantageof solubility in acrylonitrile and/or water and therefore more readilyform homogeneous cross-linked products.

Another way of obtaining cross-linked polymers is to copolymerizereactive acid or amine groups into the polymer and then react thesegroups with a bivalent or polyvalent base (metal) or acid. Reactionsbetween other reactive groups may, of course, also be used forcrosslinking purposes, e.g. ester formation between copolymerizedacrylic acid groups and glycol etc.

The exact degree of cross-linking is quite critical to the success ofthe invention. The broad idea of merely cross-linking polymers orcopolymers is, of course, well known. Two patents which mentioncross-linking would include 2,908,659 and 2,678,924. However, theseprior art patents have as their specific objective or as theirinevitable result the achieving of a degree of cross-linking whichrenders the copolymer essentially insoluble but capable of being swollenby solvents under retained shape. These patents give absolutely no hintor suggestion as to the unexpected results or desirable properties whichmight be achieved by a very limited degree of cross-linking,particularly insofar as fiber properties and the wet-spinning ofacrylonitrile copolymers is concerned. On the contrary cross-linkingpreviously has always been regarded as deterious to the fiber formingproperties of the polymer.

In accordance with this invention we have found that it is critical tohave the polymer cross-linked to a degree of 0.001 to 0.3 molar percentof cross-linking units. A narrower and more preferred range is 0.005 to0.1 molar percent. However, it is desirable to determine the optimumamount of cross-linking agent within the aboveranges depending upon theparticular cross-linker being used, the polymerization process beingused, the relative reaction rate of the agent with acrylonitrile, thedesired properties of the final product, etc. By way of example, wecarried out some experiments to determine the preferred concentrationsof certain cross-linkers for one particular discontinuous emulsionpolymerization process in water with water soluble catalysts. The lowerlimit of concentration given in the table below has been determined bythe requirements of a spinning rate of 10 m./ min. in aliphatic keroseneat 130 C. of a 20% solution of the polymer in dimethylformamide. Theupper concentration limit has been determined by the necessity ofdissolving the polymer completely in the spinning solvent and withoutformation of 'any retained swollen gel-particles. The figures are statedin moles of cross-linker used per moles of acrylonitrile. The figuresfurthermore relate to a viscometric molecular weight of about50,000-100,000 corresponding to a relative viscosity of 2.0-3.1 of 0.5%solutions of polymer in dimethylformamide. The preferred values ofmethylene bisacrylamide and triacrylohexahydrotriazine of 0.035 molepercent and 0.012 mole percent respectively refer to a molec ular weightof about 70,000 corresponding to a relative viscosity of 2.5.

When calculating the primary molecular weight M, i.e.,

is used, where mrelative viscosity in 0.5% solution of dimethylformamideand m=the average molecular weight of the monomer units.

The above given figures relate to discontinuous polymerization withlaurylsulphonate as emulsifier. In a con tinuous process withoutemulsifier about two times as much cross-linker will give the mostpreferable result e.g. 0.03 mole of triacrylylperhydrotriazine(molecular weight of 70,000).

Methylene bisacrylamide and triacrylylperhydrotriazine are thecross-linkers giving the least complications in the copolymerizationwith acrylonitrile. From the figures obtained with these twocross-linkers and from other experiments we have been able to calculateas follows. The preferred degree of real cross-linking is 1cross-linking point per 2-6 primary linear polymer molecules in the caseof a tetra-functional compound (methylenebisacrylamide), correspondingto 0.02-0.06 mole percent, and 1 cross-linking-point per 3-12 primarylinear polymer molecules in the case of a hexafunctional compound(triacrylylperhydrotriazine), corresponding to 0.005-002 mole percent.The calculated figures above refer to statistical averages counted onvalues of primary molecular weights obtained from viscometricdetermination and the amount of those poly-functional compounds whichcan be expected to react almost completely. This fact shows that thisinvention is not concerned with a fully developed insoluble net-work ofcross-linked polymer molecules but is concerned with a new type ofpolymeric molecule consisting of two or three primary linear polymericchains joined together at one point or nucleus by the polyfunctionalcompound forming a quite soluble multichain polymeric molecule with fouror six linear branches of statistically the same length going out fromone central nucleus (the original polyfunctional compound), each 100l000monomer units in length. The solvable multi-chain molecules mixed withan amount of ordinary linear chain molecules not joined together tomulti-chain-molecules form the polymeric material suited for spinning tofibers in hydrocarbons with low precipitating power. For low molecularweights high amounts of cross-linker have to be used and therelationship between primary molecular weight as determinedviscometrically and theoretical maximum amount Q of cross-linker in thepolymer in moles percent are:

where f is the number of double bonds in the cross-linker or the valencyof the ions forming salt bridges. The preferred amount of cross-linkerin the formed polymer is in practice between Q and Q/4. Depending on thepollymerization conditions one mostly has to use an amount ofcross-linker corresponding to between 2Q and Q/4 in the polymerizationprocess.

THE POLYMER SOLVENT AND THE COAGULANT In producing fibers by the methodof the present invention several known solvents for acrylonitrile may beused, such as dimethylformamide, dimethylacetamide, dimethylsulfoxide,ethylene carbonate, etc. The best fiber qualities are achieved when thepolymer solution is extruded into a hydrocarbon coagulant in which thepolymer solvent is completely soluble at the spinning temperature (-150C.) and only soluble to a limited degree at room temperature. We havefurther found that kerosene consisting essentially of aliphatichydrocarbons and free of aromatic hydrocarbons may be used as thecoagulant when dimethylformamide is used as the polymer solvent and thatthe spinning rate, when using' a gradual coagulation bath of this kindcan be considerably increased if the polymer used is cross-linked to ourspecified degree. A higher degree of stretching is thereby possible inthe coagulation bath and greatly improved mechanical properties may beobtained in the fiber, since such spinning solutions have an elasticstructure which ensures that the new-formed fiber quickly acquires arelatively high tensile strength, even if the coagulation is carried outslowly.

From cross-linked copolymers in solvents such as dimethylformamide(which show no tendency to clog the spinneret nor provoke other problemsupon-storing) it is possible, even at room temperature, to obtaintransparent 1820 and even 30 percent polymer solutions and even 30percent solutions. Such polymer solutions show a suitable viscosity forthe spinning process of about 10,000 cp. at 0, this being a suitableworking temperature in this case. It may be pointed out that thecross-linked co-polymers in accordance with this invention have asoftening temperature that may even be higher than the common one fornon-cross-linked homopolymers, which is of advantage. The speed at whichthe fiber can be spun is not reduced by using a cross-linked copolymerinstead of a cross-1inked homopolymer. Furthermore the fibers preparedfrom a cross-linked polymer by wet-spinning in kerosene show much betterphysical properties than fibers obtained from dry-spinning ofnon-cross-linked polymers. To summarize, the appropriate combination ofpolymer cross-linking and copolymerization furnishes a new method ofobtaining good solubility in solvents and spinning properties inhydrocarbon coagulants with slow coagulation power, giving as a resultan acrylonitrile fiber with greatly improved properties.

The aromatic content of the kerosene must be adapted to the solvent usedin order to get complete solubility of the polymer solvent in thekerosene at the spinning temperature. When using dimethylformamidearomatic-free kerosene may be chosen as the coagulation liquid forcross-linked polymers. When using dimethylsulfoxide and ethylenecarbonate, however, kerosene with a certain aromatic content must bechosen in order to obtain a coagulation of sufiicient strength, even inconnection with our cross-linked polymer and a spinning temperature ashigh as C. These latter solvents are very difiicult to dissolve in purealiphatic kerosene.

As stated above the composition of the hydrocarbon coagulant has to bebalanced to the polymer solvent used, which means that the preferredproportion of aliphatic hydrocarbons to aromatic hydrocarbons differsfor individual polymer solvents. In the following table the limits ofthe aromatic content in the kerosene are given for different solventsand the boiling range of the kerosene is 100-300 C., preferably -200" C.In this boiling range the refractive indeX is 1.42 for aliphatic, 1.43for hydroaromatic and 1.49 for aromatic hydrocar- The coagulationintensity may be regulated not only by the aromatic content of thekerosene and the temperature, but also by the content of the polymersolvent in the kerosene during the coagulation. This content will bebalanced by the circulation rate of the kerosene in relation to theamount of extruded spinning solution. The lower the spinning temperaturethe higher the aromatic content must be chosen. The viscosity of asolution prepared in accordance with this invention may of courseincrease due to the cross-linking as compared to a polymer which is notcross-linked. However when using nominal molecular Weights within therange of about 70,000 (determined viscometrically according toStaudinger) cross-linking in the very limited degree which we specifyabove will cause such a slight change of viscosity that 1820 and even 30percent spinning solutions can be worked up without difiiculty.Viscosity problems arise, however, when the molecular weight and thecross-linking ratio are increased above that which we specify.

SPINNING AND STRETCHING The spinning temperature should be within therange of about 80150 C., and preferably between 100 and 140 C.

Spinning of polyacrylonitrile solutions in kerosene can be achieved byparallel or counter-flow of the coagulant. Parallel flow is easier tooperate, as the coagulation power of the pure coagulant near the nozzlesis then higher and the strength of the fiber is developed more rapidly.On the other hand, counter-flow of the coagulant causes somewhat slowercoagulation power since the coagulant near the nozzles contains agreater amount of the polymer solvent. As stated before, the quality ofthe fibers formed is influenced by the coagulation power, and for thatreason, a counter-flow of the coagulant gives better fiber propertiesthan a parallel flow. It can be stated that a polymer solution(molecular weight 70,000) gave a fiber (after coagulation and stretchingto times its original length) with a strength of 3 g./ denier and 40percent break-elongation when a counter-flow of the coagulant was usedand the dimethylformamide content was about percent near the nozzles.When the same polymer solution was spun with a dimethylformamide contentof 3 percent near the nozzles, the same strength of the fiber wasobtained, but the elongation at break was only percent. Especially whenusing counter-flow of the coagulant to the spinning direction the use ofour cross-linked polymer has proved to be necessary. The controlledcross-linking which we specify above thereby indirectly causes aconsiderable improvement of the physical properties of the fiber.Spinning upwards in vertical tubes is to be preferred since the specificgravity for solvent is higher than for kerosene, and since the surfaceof the coagulant exposed to the atmosphere is thereby minimized.

As stated before, the fiber should get a stretch during the coagulationin such a way that the up-take-speed after the coagulation is higher(1.5-5 times higher) than the jet-velocity in the spinneret nozzles.This stretching can only be achieved with a cross-linked polymer if thespinning speed (coagulating speed) is to get in the economicallypreferred range of 1050 m./min.

After coagulation is complete the spun fiber should be stretched to 3-10times its length at 110-150 C. to

achieve the desired molecular-orientation. This stretch is preferablygiven the fiber while'still swollen in 3-15 percent residual solvent andcontaining 2-15 percent hydrocarbons mainly on the surface. The speed ofthe stretched fiber will therefore be 30-500 m./min. which is wellwithin the scope of viscose fiber production. This after-stretch can bedone directly after the coagulation without any wind up betweencoagulation and stretching. This is possible because the fiberscoagulated in hydrocarbons under tension are not brittle but very softand easy to handle even at high speeds, high mechanical demands and atlow temperatures. If the fiber is washed free of solvent andhydrocarbons by hot water before stretching, the fiber is more difficultto handle, the stretching rate must then be decreased or the stretchingtemperature increased to 160200 C. compared with 110140 C. in thecoagulate/d but solvent-swollen state.

The spinning of our limited cross-linked polymer in kerosene gives us afurther gain in stretching the fiber directly after coagulation at aspeed not heretofore achieved for a Wet-spun acrylic fiber.

The stretching of the fiber can be done between rollers or groups ofrollers with higher speed on the later roller or groups of rollers. Thefibers are hot enough immediately after coagulation at 130 C. to bestretched but the first roller or group of rollers ought to be heatedeither electrically or by steam inside or by hot kerosene (coagulatingbath) outside. Other heating media are, of course, also possible to use.

Our experiments have shown that a fiber coagulated in this way retainsfrom 2 to 15 percent (an average of 5 percent) of the solvent and from 2to 15 percent (an average of 5 percent) of other volatilecompoundsmainly aromatic hydrocarbons from the kerosene. The strength ofthe fiber is somewhat contingent on the molecular Weight of thepolyacrylonitrile used, and on how much the fiber has been stretched. Ifthe viscosimetric molecular weight of the polymer is about 70,000, andthe fiber is stretched between heated rollers or in the coagulationkerosene to 5 times its original length at 130 C., its strength afterspinning will be about 2.5 g./denier. The fiber will also have plasticproperties, a homogeneous circular to kidney-shaped cross section, andmoreover be as transparent as nylon or glass fibers.

REMOVAL OF THE SOLVENT AND COAGULANT LIQUID After the fiber has beenspun in kerosene and oriented, the residual solvent and liquidhydrocarbons should be removed, either in an alcohol or in hot water orby steaming at temperatures above C. (preferably at boiling point, i.e.100 C. at atmospheric pressure). This cannot be achieved quickly. Theinner parts of a fiber have been shown to retain traces of solvent andkerosene even after 15 minutes of boiling. Such traces will not aifectthe mechanical properties of the yarn but may cause uneven absorption ofthe dye. No traces of kerosene remain in the fiber after boiling for anhour and drying.

The removal of solvent and the coagulation liquid from the fiberincreases its strength from about 2.5 g./ denier to about 3.0 g./denier,and its break elongation is then 40 percent.

The subsequent drying of water treated fiber is of great importance tothe improvement of its structural properties, which vary with the dryingconditon. If the fiber is dried at a temperature below 100 C. orpreferably below C., it will in the last stage of drying become moreporous and rugged, more or less opaque and better able to carrymoisture. If dried at temperatures above C. or preferably above C.whichmay expediently be done over a hot meta-l surface-the fiber will be moretranslucent, vitreous and more compact. If the fiber before drying isboiled in a 10 percent aqueous salt-solution or washed in hot waterthoroughly before stretching it does not turn opaque even at a lowdrying temperature.

A special advantage when using kerosene hydrocarbons of the kinddescribed is that the polymer solvent and the coagulation agent are easyto separate in the spent coagulation bath by means of cooling, whichresults in phase separation of the polymer solvent and hydrocarbon. Withadmixture of a slight amount of a third component, e.g. water, the phaseseparation is facilitated. In this latter case, however, the separatedspinning solvent phase will contain some water and must be redistilled,while the kerosene needs no redistillation is it is refined throughsolvent extraction every time it is used.

The spinning technique which can be used will be more clearly understoodfrom the accompanying drawing illustrating diagrammatically a preferredapparatus suitable for use in producing fibers according to thisinvention.

Referring to the drawing the reference numeral 1 indicates a multiholespinneret through which an acrylonitnile polymer solution is extrudedinto a coagulating bath 2 contained in a vertical tube 3 of 3 In. heightprovided with a steam jacket. In its travel through the coagulating baththe yarn 4 formed by the coagulation of the polymer solution issubjected to tension directly from the spinneret by means of apositively driven up-take roller or feed wheel 5 with a peripheral speedpreferably higher than the jet velocity of the solution in thespinneret. The yarn is then passed directly through a stretching device6 comprising two groups of heated godets of different peripheral speed.The first group 7 of the heated godets has a peripheral speed of 30 m.per minute and the second group 8 a speed of 150 m. per minute. Thetemperature of the first group 7 of godets is preferably 140 C. and ofthe second group 8 between room temperature and 140 C. After thestretching device 6 the yarn is led through a crimper 8 and a cutter andthen to a washing and crimp-fixation device 11. The crimper 9 and cutter10 are of conventional type. The washing and crimp-fixation device 11 isof shaft type with inlet for steam and outlet for recovery of thepolymer solvent and coagulant (not shown). The crimp fixation isachieved by treating the crimped fiber with 100130 C steam. From thewashing and crimp-fixation device 11 the washed and cnimped staple fiberis dried in a drying and heat-conditioning apparatus 12 comprising anendless conveyor 13 in a heated chamber 14. The treated staple fiber isthen led through an opening device 15 to obtain the ultimate product Thedrawing also illustrates one way of introducing the liquid hydrocarboncoagulant, e.g. kerosene. The coagulant liquid is stored in tank 16 andtherefrom led to the upper parts of the vertical spinning tube 3. Thespent coagulating bath is led out of the tube 3 at the bottom and by apump 17 for recovery of the polymer solvent and the coagulant for reuse.

EXAMPLES The following examples are illustrative of preferredembodiments of the present invention. It should be understood that theseexamples are not intended to limit the invention and that obviouschanges may be made by those skilled in the art without changing theessential characteristics and the basic concept of the invention. Theparts and percentages are by Weight, the temperature is room temperatureand the pressure is atmospheric, unless otherwise indicated.

Example 1 A first copolymer was prepared from a mixture of 97 kg.acrylonitrile, 3 kg. acrylic acid and 120 g. methylene bisacryloamide inthe following manner. The monomer mixture was gently poured during 3hours into 400 liters of water at to C. containing dissolved 1 g.amrnoniurnpersulfate, 1.5 g. sodiumpyrosulfite and 1 g.sodiumlaurylalcoholsulfate per liter. The polymerization was continued 4hours and a yield of 95 kg. precipitated and dried polymer was obtained.The copolymer had :a molecular weight of 60,000-65,000 according toStaudinger.

Example 2 An 18 percent solution in dimethylformamide was prepared fromthe copolymer made in accordance with Example 1 and the solution wasextruded without any preheating through a 1000 hole spinneret(hole-diameter 0.15 mm.) at a velocity of 250 ml. per minute. Thespinneret was arranged in the bottom of a vertical steam-mantled tube of3 m. length, through which an aromatic-free kerosene (boiling range160220 C.) with a temperature of 130 C. running from above to the bottom(counterflow). The velocity of the collecting godet in the upper part ofthe tube was 30 in. per minute. After said godet the fiber was stillimmersed in kerosene at 130 C. and the fiber was stretched 5 times itsoriginal length to another godet with a peripheral speed of 150 m. perminute. After that the fiber was allowed to relax at 130 C. in air andwas then crimped and cut to staple fibers. The product was washed withboiling water containing a nonionactive soap (Berol Wasc) for 30minutes, at pH 4, to remove 8 percent of dimethylformamide and 10percent of kerosene, rinsed, prepared with a cationactive agent (Sapamin0C) and dried in air at C. The fiber had a denier of 3.0 (measuredmicroscopically 3.1 to 3.2), its tensile strength was 3.0 g. per denierand elongation at rupture about 40 percent. The dye receptivity to basicdyes, for example Du Ponts Basic Blue, was excellent. The amount ofsaturation was about 10 percent dye in the fiber. Fed into the tube at arate of 1200 ml./min. the kerosene will contain 15 percent dimethylformamide when passing out at the bottom. When cooled to 15 C., theprecipitating bath is separated into a dimethyl formamide phase and akerosene phase which latter is almost colorless and contains 2.5 percentof dimethyl formamide and can again be directly fed into the tube at thetop. If kerosene is washed by meeting a flow of only 3 percent of waterby weight of the kerosene, its dimethyl formamide content will bedecreased to 0.1 percent. The dimethyl formamide phase may on the otherhand be distilled to reduce its hydrocarbon contents from 5 to 1.0percent. It is hardly practicable to separate the remaining 1 percent ofhydrocarbons by distillation considering the azeotropic conditionsarising during the distillation. More hydrocarbons can, however, beremoved if the dimethyl formamide phase is mixed with the waterpreviously used to wash the kerosene, and the hydrocarbon content of thedimethyl formamide can then be reduced by distillation to less than 0.1percent.

Example 3 A copolymer prepared according to Example 1 was also dissolvedin dimethylsulphoxide and spun at C. in Sangajol kerosene from the ShellOil Company. Other conditions were similar to those in Example 2, andthe separation of solvent from kerosene followed in the same manner.Sangajol kerosene is a kerosene containing about 60 percent ofaromatics. The yarn obtained after boiling in water and drying at 60 C.showed about the same properties as in Example 2 but was of even whiterappearance.

Example 4 A second copolymer was prepared from a mixture of 95 kg.acrylonitrile, 5 kg. methacrylate and 60 g. triacrylylhexahydrotriazine(as cross-linking agent) in the following manner. The monomer mixturewas gently poured during 3 hours into 400 liters of water at 50 to 55 Ccontaining dissolved 1 g. ammoniurnpersulfate, 1.5 g. sodiumpyrosulfiteand 1 g. sodiumlaurylalcoholsulfate per liter. The polymerization wascontinued 4 hours and a yield of 95 kg. precipitated and dried polymerwas obtained. The copolymer had a molecular weight of 60,000- 65,000according to Staudinger.

Example 5 An 18 percent solution in dimethylformamide was prepared fromthe copolymer made in accordance with Ex- 1 l ample 4 and the solutionwas extruded without any preheating through a 1000 hole spinneret(hole-diameter 0.15 mm.) at a velocity of 250 ml. per minute. Thespinneret was arranged in the bottom of a vertical steam-mantled tube of3 m. length, through which an aromatic-free kerosene (boiling range160220 C.) with a temperature of 130 C. was running from above to thebottom (counterflow). The velocity of the collecting godet in the upperpart of the tube was 30 m. per minute. After said godet the fiber wasstill immersed in kerosene at 130 C. and the fiber was stretched 5 timesits original length to another godet with a peripheral speed of 150 in.per minute. After that the fiber was allowed to relax at 130 C. in airand was then cut upon crimping to staple fibers. The product was washedwith boiling water containing a nonionactive soap (Berol Wasc) for 30minutes, at pH 4, to remove 8 percent of dimethylformamide and 10percent of kerosene, rinsed, prepared with a cationactive agent (SapaminOC) and dried in air at 120 C. The fiber had a denier of 3.0 (measuredmicroscopically 3.1 to 3.2), its tensile strength was 3.0 g. per denierand elongation at rupture about 40 percent. The dye receptivity to basicdyes, for example Du Ponts Basic Blue, was excellent. saturation wasabout 8 percent dye for the methylacrylate containing fiber. Fed intothe tube at a rate of 1200 mL/min. the kerosene will contain percent ofdimethyl formamide when passing out at the bottom. When cooled to 15 C.,the precipitating bath is separated into a dimethyl formamide phase anda kerosene phase which latter is almost colorless and contains 2.5percent of dimethyl formamide and can again be directly fed into thetube at the top. If kerosene is washed by meeting a flow of only 3percent of water by weight of the kerosene, its dimethyl formamidecontent will be decreased to 0.1 percent. The dimethyl formamide phasemay on the other hand be distilled to reduce its hydrocarbon contentsfrom 5 to 1.0 percent. It is hardly practicable to separate theremaining 1 percent of hydrocarbons by distillation considering theazeotropic conditions arising during the distillation. More hydrocarbonscan, however, be removed if the dimethyl formamide phase is mixed withthe water previously used to wash the kerosene, and the hydrocarboncontent of the dimethyl formamide can then be reduced by distillation toless than 0.1 percent.

Example 6 A copolymer prepared according to Example 4 was also dissolvedin dimethylsulphoxide and spun at 130 C. in Sangajol kerosene from theShell Oil Company. Other conditions were similar to those in Example 5,and the separation of solvent from kerosene followed in the same manner.Sangajol kerosene is a kerosene containing about 60 percent ofaromatics. The yarn obtained after boiling in water and drying at 60 C.showed about the same properties as in Example 5 but was of even whiterappearance.

Example 7 A third copolymer was prepared from a mixture of 97 kg.acrylonitrile and 3 kg. of acrylic acid using the same general processoutlined in Example 1, but with the exception that no cross-linkingagent such as methylene bisacryloa-mide was used. The molecular weightof copolymer was about 58,000. A percent solution of this copolymer indimethylforma rnide was prepared but the solution could not be extrudedand spun by following the procedure outlined in Example 2. By using akerosene which had about 15 percent aromatics and a boiling range ofabout 150210 C. (as opposed to an aromatic-free kerosene) it waspossible to achieve a spinning rate (i.e. collecting velocity) of 3 m.per minute without fiber rupture. This was much lower than the spinningrate achieved in Example 1 and it is thus seen that the presence of thevery small amount of cross-linking agent set forth in Example 1 made avery great difiference in spinning rate.

The amount of l 2 Example 8 A fourth copolymer was prepared from amixture of 97 kg. acrylonitrile and 3 kg. of acrylic acid using the samegeneral process outlined in Example 1, but with the exception that theamount of cross-linking agent (methylene bisacryloamide) was increasedto 0.5 molar percent. The molecular weight of the copolymer was about75,000. This copolymer could not be satisfactorily dissolved indimethylformamide and the resulting solution showed typicalgel-particles. A small steel ball when dropped through a 20 percentsolution did not descend exactly vertically but showed some irregularmovements in the horizontal direction depending on big gel-particlesdispersed in the continuous medium of polymer solution. In trying tospin this solution it was possible to start up the operation but afteronly a few minutes several holes of the spinneret were clogged and aspinning could not be continued.

Another polymer was prepared by exactly the same procedure with theexception that the amount of cross-linking agent was 1.0 molar percent.This polymer was so insoluble in dimethyltormamide that it was not evenpossible to get a homogeneous 0.5 percent solution for determination ofthe molecular weight and it therefore could of course not be extrudedand spun into filaments.

Example 9 A fifth copolymer was prepared from a mixture of kg.acrylonitrile and 5 kg. of methylacrylate using the same general processoutlined in Example 4, but with the exception that no cross-linkingagent such as triacrylohydrotriazine was used. The molecular weight ofcopolymer was about 60,00065,000. An 18 percent solution of thiscopolymer in dimethylforrnamide was prepared but the solution could notbe extruded and spun by following the procedure outlined in Example 5.By using a kerosene which had about 15 percent aromatics and a boilingrange of about -210 C. (as opposed to an aromatic-free kerosene) it waspossible to achieve a spinning rate (i.e. collecting velocity) of 3 m.per minute without fiber rupture. This was much, much lower than thespinning rate achieved in Example 5 and it is thus again seen that thepresence of the very small amount of crosslinking agent set forth inExample 4 made a very great diiference in spinning rate.

Example 10 A sixth copolymer was prepared from a mixture of 95 kg.acrylonitrile and 5 kg. of methylacrylate using the same general processoutlined in Example 4, but with the exception that the amount ofcross-linking agent (triacrylohydrotriazine) was increased to 1.0 molarpercent. The molecular weight of copolymer was estimated to be about50,000 but the cloudy solution was too inhomogeneous to allow amolecular weight calculation on the basis of viscosity. This copolymershowed the same spinning trouble as did the polymer in Example 8.Examination of the spinneret after trying to start the spinning fivetimes without practical success showed that the inside of the spinneretwas covered with gel-lumps pressed against the spinneret and partlyforced into the holes of the spinneret, thereby clogging same. Thegel-lumps had to be removed mechanically from the spinneret as they wereinsoluble. In dimethylformamide they formed insoluble slime-like lumps,and these lumps did not even dissolve upon initially boiling at 153 C.but the lumps did turn more yellow and did break down into smaller lumpsafter heating for a number of minutes at 153 C.

This clearly demonstrates that the maximum amount of the cross-linkingagent is quite critical insofar as producing a spinnable fiber isconcerned.

Example 11 An emulsion of the copolymer prepared according to Example 1,but without the addition of methylenebisacryloamide, was treated with 1kg. of aluminiumsulfate at 50 C. for 30 minutes at pH 6. The copolymerwas found to contain 0.04 percent aluminium after this treatment. Whenspinning such a copolymer according to Example 2 in kerosene containing15 percent of aromatics the collecting velocity of 50 m. per minutecould be used, or if stretched 5 times its coagulated length 250 in. perminute. Similar spinning values were obtained upon treatment withmagnesium sulfate, the fiber being in this case more discolored.

FIBER PROPERTIES Fibers made of our limited cross-linked copolymers showmore valuble properties than acrylic fibers made of common linearpolymers. The fiber properties at room temperature do not differ verymuch but the properties at elevated temperatures and wet conditions arehighly improved. Below we have presented some comparable figuresconcerning a fiber A made of the limited crosslinked copolymer ofExamples 4 and 5 and a fiber B of a linear copolymer of the samecomposition as of Example 4 Without any cross-linking '(compare Example9).

Tensile strength, g./den., 20 0.; 60 RH 3.0 2, o Elongation at break,percent, 20 0.; 60 R.H 35 35 Modulus, g./den., 20 0.; 60 R.H 45 40Tensile strength, g./den., 90 0., wet .1 1. 3 0. 5 Elongation at break,percent, 90 0., wet 60 110 Modulus, g./den., 90 0., wet 2.5 1.1 Tensilestrength, g./den., 150 0., dry 0. 8 0. 2 Zero strength temperature, H320 210 Orientation angle according to X-ray measurement, C 54 30Crystallinity, percent 19 19 Torsional fatigue, cycles 1,000 100 Wearstrength dry, cycles 2, 600 1,010 Wear strength wet, cycles n 3, 700 950Soil resistance (percent residual reflectance after 10,000

steps) 98. 78. 5

The figures above illustrate the vastly improved fiber propertiesespecially under hot-wet conditions, which are particularly importantfor technical textiles and for the behavior of the fiber during dyeing,drying and other hot and wet textile processes. Goods and fabrics madeof fiber A show improved wrinkle recovery, improved dimensionalstability and also improved pleat retention compared with fabrics madeof fiber B. In practical use the soil resistance for fiber A is veryremarkable, but as mentioned before this property is not onlyattributable on the multi-chain structure but also to the specificcoagulation in hydrocarbons. It can further be emphasized that the goodhot-wet properties can be found only in fibers produced from polymerscross-linked during the polymerization process. If the polymer iscross-linked by formation of salt bridges between acidic groupsincorporated in the polymer, the resulting fiber shows the same badhotwet properties as fiber B. Only at 150 C. dry conditions does thisfiber show some improved properties. The salt bridges therefore seem tobe sensitive to hydrolysis by water and are inferior to cross-linking bypolyunsaturated compounds in the polymerization process.

Those skilled in the chemical arts, and particularly in the art to whichthis invention pertains, will readily appreciate that many modificationsof the basic invention set forth here are possible. For example, it isquite possible that other closely related compounds might work as wellas the herein specifically described compounds and there would certainlybe no invention involved in trying such closely related compounds, inview of the present broad disclosure. All of these modifications areconsidered to be within the scope of the present claims 14 by virtue ofthe well-established doctrine of equivalents.

This is a continuation-in-part of our prior application Serial No.539,558 filed on October 10, 1955, and now abandoned.

We claim:

1. A fiber-forrning composition of matter which is soluble in a polymersolvent selected from the group consisting of dimethylformamide,dimethylacetamide, dimethylsulfoxide, butyrolacetone, ethylene carbonateand dimethyl methoxyacetamide comprising an acrylonitrile copolymercontaining at least molar percent of acrylonitrile units and up to about15 molar percent of a monoethylenically unsaturated monomer selectedfrom the group consisting of vinyl acetate, vinyl chloride, vinylidenechloride, acrylic acid, acrylamide, methacrylonitrile, methacrylamideand an ester of an acid selected from the group consisting of acrylicacid and methacrylic acid, and cross-linked to a degree of from 0.001 to0.3 molar percent of cross-linking units by a cross-linking agentselected from the group consisting of divinyl benzene,methylene-bisacryla mide, diallylphthalate, diallylmaleate, ethyleneacrylate, ethylene diacrylate and triacrylylperhydrotriazine.

2. A process for preparing a soluble acrylonitrile c0- polymer for thespinning of fibers, comprising reacting a mixture containing at least 85molar percent of acrylonitrile, up to 15 molar percent of amonoethylenically unsaturated monomer selected from the group consistingof vinyl acetate, vinyl chloride, vinylidene chloride, acrylic acid,acrylamide, methacrylonitrile, methacrylamide and an ester of an acidselected from the group consisting of acrylic acid and methacrylic acid,and from 0.005 to 0.1 molar percent of a cross-linking polyethylenicallyunsaturated monomer selected from the group consisting of divinylbenzene, methylenebisacrylamide, diallylphthalate, diallylmaleate,ethylene acrylate, ethylene diaerylate and itriacylylperhydrotriaziine,in the presence of a polymerization catalyst.

3. A fiber-forming composition of matter which is soluble in a polymersolvent selected from the group consisting of dimethylformamide,dimethylacetamide,, dimethylsulfoxide, butyrolacetone, ethylenecarbonate and dimethyl methoxyacetamide comprising an acrylonitrilecopolymer containing at least 85 molar percent. of acrylonitrile unitsand up to about 15 molar percent of a monoethylenically unsaturatedmonomer selected from the group consisting of vinyl acetate, vinylchloride, vinylidene chloride, acrylic acid, acrylamide,methacrylonitrile, methacrylamide and an ester of an acid selected fromthe group consisting of acrylic acid and methacrylic acid, andcross-linked to a degree of from 0.00 5 to 0.10 molar percent ofcross-lin king units by a cross-linking agent selected from the groupconsisting of divinyl benzene, methylenebisacrylamide, diallylphthalate,diallylmaleate, ethylene acrylate, ethylene diacrylate andtriaerylylperhydrotriazine.

4. A fiber-forming composition of matter comprising an acrylonitrilecopolymer containing at least 85 molar percent of acrylonitrile unitsand up to about 15 molar percent of a monoethylenically unsaturatedmonomer and cross-linked to a degree corresponding to about 1 crosslinkper 2-12 straight polymeric molecules.

5. A fiber-forming composition according to claim 4 in which theacrylonitrile polymer is cross-linked by means of a compound of thegroup consisting of divinyl benzene, triacrylylperhydrotriazine,methylenebisacryloamide, diallylphthalate, diallylmaleate and ethyleneacrylate.

6. A fibenforming composition according to claim 4 wherein thecross-linked acrylonitrile polymer is a copolymer of acrylonitrile and amonofunctional unsaturated monomer selected from the group consisting ofvinyl acetate, vinyl chloride, vinylidene chloride, acrylamide,methacrylonitrile, methacryloamide, an ester of acrylic acid and anester of methacrylic acid.

References Cited by the Examiner UNITED STATES PATENTS DA lelio 26086.1Merion et a1 28-82 Chaney 260-887 Richards 260-887 'Drechsel et a1260-805 Shokal 260-755 Graulich et a1. 260-855 JOSEPH L.

DAlelio 260-935 Ham 260-785 Marley 28-82 Terpay 18-54 Hooper 18-54Markus 260-785 Shashoua 260-32.6

SCHOFER, Primary Examiner. v. BRINDISI, LEON J. BERCOVITZ, Examiners.

C. B. HAMBURG, L. WOLF, Assistant Examiners.

1. A FIBER-FORMING COMPOSITION OF MATTER WHICH IS SOLUBLE IN A POLYMERSOLVENT SELECTED FROM THE GROUP CONSISTING OF DIMETHYLFORMAIDE,DIMETHYLACETAMIDE, DIMETHYLSULFOXIDE, BUTYROLACETONE, ETHYLENE CARBONATEAND DIMETHYL METHOXYACETAMIDE COMPRISING AN ACRYLONITRILE COPOLYMERCONTAINING AT LEAST 85 MOLAR PERCENT OF ACRYLONITRILE UNITS AND UP TOABOUT 15 MOLAR PERCENT OF A MONOETHYLENICALLY UNSATURATED MONOMERSELECTED FROM THE GROUP CONSISTING OF VINYL ACETATE, VINYL CHLORIDE,VINYLIDENE CHLORIDE, ACRYLIC ACID, ACRYLAMIDE, METHACRYLONITRILE,METHACRYLAMIDE AND AN ESTER OF AN ACID SELECTED FROM THE GROUPCONSISTING OF ACRYLIC ACID AND METHACRYLIC ACID, AND CROSS-LINKED TO ADEGREE OF FROM 0.001 TO 0.3 MOLAR PERCENT OF CROSS-LINKING UNITS BY ACROSS-LINKING AGENT SELECTED FROM THE GROUP CONSISTING OF DIVINYLBENZENE, METHYLENEBISACRYLAMIDE, DIALLYLPHTHALATE, DIALLYLMALEATE,ETHYLENE ACRYLATE, ETHYLENE DIACRYLATE AND TRIACRYLYLPERHYDROTRIAZINE.